Device never wakes on program run following sketch upload

[disk91]

After uploading a sketch to my MKR FOX 1200, the following code never wakes up after the first sleep call (LED remains on):

#include <ArduinoLowPower.h>
void setup() {
  pinMode(6, OUTPUT);
}

void loop() {
  digitalWrite(6, HIGH);
  LowPower.sleep(500);
  digitalWrite(6, LOW);
  LowPower.sleep(500);
}

The fault only occurs under the specific conditions of the program running after a sketch upload has been performed. If I power cycle the board, it works correctly.

Additional context

• Device never wakes on program run following sketch upload #5 (comment)

[facchinm]

Hi @disk91 ,
this may depend on your operating system/USB connection; the code path in case of USB connection is quite different from the normal one.
Could you try reverting 8cf4c73 and see if the behaviour is the expected one (in your setup)?

[sjernigan]

We are seeing a similar problem. We also see that sometimes the first sleep call almost immediately returns.
Current Setup: Feather M0, using Mac to program/power, reverted the commit above as asked--
When powered from a battery (no data signal), the first call immediately returns, subsequent calls work correctly. Same for power by mac after unplugging. However, after you reprogram, the first call will never return. The reset button continues the previous behavior (ie., it does not change it to the unplugged/replug behavior).

[sslupsky]

I think I have this problem as well. I think it may have something to do with the rtc. Recently I added an rtc.begin() in my setup() and this has stopped the OP’s issue from happening.

[sslupsky]

I found another reference to this issue:

https://forum.arduino.cc/index.php?topic=499101.0

Gormd reported that using LowPower.attachInterruptWakeup() also cleared this up. Seem's to me there is a bug here related to declaration or construction of the RTC object?

[DanielRIOT]

You could call
SerialUSB.end(); just before calling LowPower.sleep();
to stop the USB interrupts from happening and continuously waking the system

[nekuneko]

Hi @disk91 ,
this may depend on your operating system/USB connection; the code path in case of USB connection is quite different from the normal one.
Could you try reverting 8cf4c73 and see if the behaviour is the expected one (in your setup)?

@facchinm Is there any reason to use USBDevice.standby(); call ? I think it doesn't work in the propper way and in order to avoid issues, I would leave sleep() function simply as this:

void ArduinoLowPowerClass::sleep() {
	USBDevice.detach();
	SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;
	__DSB();
	__WFI();
       USBDevice.attach();
}

If standby is used, wouldn't it be necessary to have a function to "resume" and call runInStandby() as well standby function calls noRunInStandby()?